(1) Field of the Invention
The present invention relates to a method for manufacturing a resin pattern and a method for vacuum sealed molding process using the resin pattern, especially, to the method for manufacturing the resin pattern preferable for general casting, and molding using the pattern such as plastic molding and silicone rubber molding, and the method for vacuum sealed molding process using the resin pattern same.
(2) Description of the Prior Art
Conventionally, a method for vacuum sealed molding process using wooden patterns has been generally used (JP-A-49-87521 (1974)) for manufacturing, for example, of bearing brackets of traction motors for locomotives by casting.
First, a wooden pattern having same shape as an upper half or a lower half of a steel casted final product is manufactured. When manufacturing the wooden pattern, a wooden plate is cut out in a shape of the steel castings and patterns of all members are manufactured in order to form the same shape as the upper half or the lower half of the steel casted final product, and subsequently, the patterns of the members are assembled in the same shape as the upper half or the lower half of the steel casted final product. Further, necessary vents for subsequent vacuum sealed molding process are provided to the wooden patterns by drilling. A plurality of the wooden patterns having the same shape as the upper half or the lower half of the steel casting are prepared by the same method as the above described method, and the wooden patterns of the upper half and the lower half are combined together and are used for manufacturing the steel casting by the vacuum sealed molding process.
Next, the vacuum sealed molding process is explained.
First, the combined wooden pattern is fixed on a hollowed surface plate (a vacuum box) and is covered with a film, for example, a thin plastic film having a large elongation percentage and a high plastic deformation rate. The film is softened by heating, and the softened film is made to contact tightly on surface of the wooden pattern by suction through the vents in the wooden pattern with reducing pressure of the vacuum box. Subsequently, the wooden pattern tightly covered by the film is enclosed with flasks which have a means for reducing pressure, a predetermined amount of dried sand which has controlled grain sizes is filled into the flask with vibration, and surface of the dried sand which is filled in the flask is covered with same film as above described. Then, the pressure in the vacuum box is increased to atmospheric pressure so as to release the tight contact of the film on the surface of the wooden pattern, farther, the dried sand in the flask is hardened by reducing pressure in the flask through a means for reducing pressure which is furnished to the flasks, and a drag which has same fabrication plane as the wooden pattern on remained surface of the dried sand is formed by tearing off the wooden pattern from the dried sand. The drag and a cope which is formed by the same method as above described method are combined together, and molten metal is poured into an internally formed mold cavity (fabrication plane). And after the molten metal is solidified, the reduced pressure in the flask is returned to atmospheric pressure. The dried sand regains fluidity again by returning to atmospheric pressure, and casting product can be completed by recovering of the sand. Besides, the wooden pattern can be used repeatedly in the vacuum sealed molding process, and the same casting product as the above described product can be manufactured in mass production. The recovered dried sand can be used again after cooling.
However, the conventional vacuum sealed molding process had such various problems as described hereinafter because of using wooden pattern. That is, as many wooden members are integrated together to form the wooden pattern, the above described film is broken by contacting planes and grains of the wooden members when tearing off the wooden pattern from the dried sand. Farther, after repeated usage of the wooden pattern, faults in dimensions of the casting product are caused by secular deterioration (distortion by abrasion, breakage, dehydration, and humidification), and refabrication of the mold and correction of the casting product by hands become necessary. Farther, the wooden pattern used in the vacuum sealed molding process is to be drilled vents for decreasing pressure in order to contact a film tightly on surface of the wooden pattern, but conventionally, manufacturing of the vents have been performed by hands and necessitated a very long time. And, as the wooden pattern was manufactured one by one by hands, cost of the manufacturing became remarkably expensive when a large number of the wooden patterns were manufactured.